Advanced Materials Research Vols. 602-604

Abstract: The effect of different annealing temperature on microstructure and properties of the hot-stamping boron steel were studied.The results show that the yield strength of the test steel is reduced with increasing annealing temperature, only at 790°C,the specimen yield strength increased slightly, and showed a significant downward trend after 790°C.The specimen tensile strength and hardness with the change of the same trend when annealing temperature changes.And through the test we can see,at 760°C ,the test steel has entered a two-phase region,the test steel gain ferrite and pearlite when it is annealed below the temperature,it is easy to appear martensite microstructure when it is annealed in the higher temperature,and lead to the strength and hardness of the rise.

Abstract: The inclusions will be controlled in the plastic region effectively when the slag basicity is in the range of 0.5~1.2 and Al2O3 content in the range of 10%~25% according to thermodynamic calculation. The results of laboratory research show that the value of (CaO+MgO)/SiO2 and Al2O3 content will rise up with the increase of [Als]. Therefore, [Als] should be less than 6×10-6. Furthermore, inclusions in steel cord will be controlled plastically in laboratory with the slag basicity in the range of 0.8~1.0 and Al2O3 content in the range of 0%~10%.

Abstract: Using refining agent to proceed refining treatment on dual-phase wear-resistant steel, the refining agent is made up of CaO, CaF2, Al2O3, Al, Na2CO3 and BaCO3. The experimental furnace is 25kg vacuum induction furnace, stalling 10 minutes after adding the refining agent, the heating temperature is between 1550 and 1600°C. By doing this, the content of harmful impurities including O, N and S in the steel is significantly reduced and the mainly existing form of the main non-metallic inclusions is changed, it also reduces the size and number of the microstructure of the inclusions in the steel and improves the impact toughness and elongation of dual-phase wear-resistant steel significantly.

Abstract: Isothermal constant strain rate compression tests on high-carbon steel are carried out under strain rate of 1s-1, 10s-1 and 50s-1 respectively and deformation of 0.7 using the THERMECMASTOR-Z thermal simulator at a temperature of 1000°C. The austenite grain morphology before and after deformation and the true stress-strain curves during the deformation process are analyzed. The experimental results show that increased strain rate can obviously contribute to the grain refinement, and when the strain rate is at low level (e.g. 1s-1)，increased strain rate can further help refine the grains. And under the same temperature conditions, as the deformation rate rises, peak stress will move toward the direction of strain increment，thus the dynamic recrystallization is not apt to occur.

Abstract: The microstructures and hardness of spray-formed and aged H13 steel were investigated by OM, SEM, XRD and hardness tester. Compared to the as-cast H13 steel, the microstructures of the spray-formed H13 steel is characterized by lower bainite, martensite and much more retained austenite, inducing lower hardness than the as-cast H13. The peak aging temperature for the spray-formed H13 steel is 50°C higher than the commercial H13 steel (500°C) for their different microstructures. After aged at 550°C for 50h, a much higher hardness (about 53 HRC) can be retained in the spray-formed H13 steel, showing an excellent thermal stability at 550°C.

Abstract: The effect of quenching medium on the microstructure and mechanical properties has been investigated for the 42CrMo steel, which is used in a polar crane for the nuclear power station. Experimental results indicates that the microstructure of the air quenched 42CrMo steel is pearlite , proeutectoid ferrite and a small amount of upper bainite. The microstructure of 42CrMo after oil quenching is lower bainite and martensite, and changed to martensite and a small amount of lower bainite after water quenching. The Charpy impact energy at -12°C of the air ,oil and water quenched samples after 560°C tempering is 12J, 22J and 59J, respectively. The decrease of proeutectoid ferrite significantly improves the Charpy impact energy of the investigated steel. The strength and impact property of 42CrMo under water quenching together with 560°C tempering can meet the requirements of the wheel and level wheel for the polar crane.

Abstract: Welding thermal cycle of SMA490BW corrosion resistance steel with different heat inputs were simulated by using Gleeble-3500 thermo-mechanical simulator to investigate the grain size of the heat affected zone (HAZ). Results show that welding heat cycle peak temperature has great influence on the grain size with the same other conditions, the higher peak temperature is the bigger grain size is; in different welding thermal cycling conditions, line energy affects grain size differently; specimens which experienced two thermal cycle have smaller grain size than which experienced just one thermal cycle.

Abstract: In this paper, the corrosion behavior was researched which was happen on the 304,321,316Lect. stainless steel materials in the analogue situation of calcining gas atmosphere of ammonium paramolybdate.The oxidized etch which happened on the sample’s surface, phase constituent and element content of the fracture surface, was analyzed by the means of SEM、XRD.The results showed that the phases of Fe2(MoO4)3,MoO3,MoO2.5(OH)0.5,Cr2O3,Cr2Ti5O13, Fe2O3,Fe3O4 ect. are contained on the surfaces of the 304,316L, 321 samples which are calcined. There is an inside oxidized corrosion layer in 304 316L. The oxidizing film is damaged and the oxygen penetrates into the base to form an oxidized layer. A thin and compact oxidation film was formed between 321 corrosion layer and the alloy interface, which have prevented the base from further corrosion, under this experiment conditions, this steel belonged to the inoxidizability materials. The coating deficiency of 321 steel is shallow; the particles of oxidate is thin and without inner corrosion; the weight gain rate of oxidized etch is slow (average rate 5.2×10-2mg/ (cm2•h)), the weight gain is less and corrosion resistance is fine.

Abstract: The microstructure, tensile and impact property of a 600 MPa HSLA steel plate at different temperature were investigated by tensile and impact tests, metallographic observation, SEM and EDX analysis. The results indicated that the microstructures of the steel after tensile tests were mainly the bainites. As the temperature increased from 300°C to 650°C, the yield strength and tensile strength decreased, the elongation and reduction of area increased, but this steel had a relatively stable tensile property below 400°C. Moreover, as the temperature reduced from 20°C to -80°C, the impact toughness was gradually decreased, and the ductile-brittle transition temperature of this steel was obtained at -57.75°C by using Boltzmann function fitting.

Abstract: The low cycle fatigue (LCF) behavior of Q235 steel under mean strain control has been investigated. A serious of the strain controlled cyclic loading experiments with several combinations of strain amplitudes and mean strains have been performed. Significant cyclic hardening and mean stress relaxation were observed in all cases. Fractography by scanning electron microscopy (SEM) was used to determine the LCF failure mechanisms and fatigue crack propagation modes of the Q235 steel.